perhaps I am shifting the goalpost slightly here, but there is at least one publisher that makes all of its books available to read online:http://www.openbookpublishers.com/
sadly, it does not work on an ereader (at least not on mine), but though you cannot download anything for free, you can read the whole book online if you wish.

Granted, in these cases authors are academics who earn their crust in other way, but at least these are not of the types that try to make a buck (or substantially more) by cutting it into the "principle of" textbooks markets. At least in academia, research production should be made available for free!